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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.CompletionCondition"></a><a class="link" href="CompletionCondition.html" title="Completion condition requirements">Completion
      condition requirements</a>
</h3></div></div></div>
<p>
        A <span class="emphasis"><em>completion condition</em></span> is a function object that is
        used with the algorithms <a class="link" href="read.html" title="read"><code class="computeroutput"><span class="identifier">read</span></code></a>, <a class="link" href="async_read.html" title="async_read"><code class="computeroutput"><span class="identifier">async_read</span></code></a>, <a class="link" href="write.html" title="write"><code class="computeroutput"><span class="identifier">write</span></code></a>, and <a class="link" href="async_write.html" title="async_write"><code class="computeroutput"><span class="identifier">async_write</span></code></a> to determine when the
        algorithm has completed transferring data.
      </p>
<p>
        A type <code class="computeroutput"><span class="identifier">X</span></code> meets the <code class="computeroutput"><span class="identifier">CompletionCondition</span></code> requirements if it
        satisfies the requirements of <code class="computeroutput"><span class="identifier">Destructible</span></code>
        (C++Std [destructible]) and <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
        (C++Std [moveconstructible]), as well as the additional requirements listed
        below.
      </p>
<p>
        In the table below, <code class="computeroutput"><span class="identifier">x</span></code> denotes
        a value of type <code class="computeroutput"><span class="identifier">X</span></code>, <code class="computeroutput"><span class="identifier">ec</span></code> denotes a (possibly const) value of
        type <code class="computeroutput"><span class="identifier">error_code</span></code>, and <code class="computeroutput"><span class="identifier">n</span></code> denotes a (possibly const) value of type
        <code class="computeroutput"><span class="identifier">size_t</span></code>.
      </p>
<div class="table">
<a name="boost_asio.reference.CompletionCondition.t0"></a><p class="title"><b>Table 9. CompletionCondition requirements</b></p>
<div class="table-contents"><table class="table" summary="CompletionCondition requirements">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  expression
                </p>
              </th>
<th>
                <p>
                  return type
                </p>
              </th>
<th>
                <p>
                  assertion/note<br> pre/post-condition
                </p>
              </th>
</tr></thead>
<tbody><tr>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">x</span><span class="special">(</span><span class="identifier">ec</span><span class="special">,</span>
                  <span class="identifier">n</span><span class="special">)</span></code>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput"><span class="identifier">size_t</span></code>
                </p>
              </td>
<td>
                <p>
                  Let <code class="computeroutput"><span class="identifier">n</span></code> be the total
                  number of bytes transferred by the read or write algorithm so far.<br>
                  <br> Returns the maximum number of bytes to be transferred on
                  the next <code class="computeroutput"><span class="identifier">read_some</span></code>,
                  <code class="computeroutput"><span class="identifier">async_read_some</span></code>,
                  <code class="computeroutput"><span class="identifier">write_some</span></code>, or
                  <code class="computeroutput"><span class="identifier">async_write_some</span></code>
                  operation performed by the algorithm. Returns <code class="computeroutput"><span class="number">0</span></code>
                  to indicate that the algorithm is complete.
                </p>
              </td>
</tr></tbody>
</table></div>
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